Hydration Fingerprints: A Reproducible Protocol for Accurate Water Uptake in Anion-Exchange Membranes

Anion-exchange membranes (AEMs) not only enable the fabrication of catalyst-coated membranes without precious metals but are also projected to achieve a technology-readiness level (TRL) suitable for industrial deployment before the end of this decade. Accurate and reproducible water uptake data are essential for guiding AEM design, yet conventional gravimetric methods-relying on manual blotting and loosely defined drying steps-can introduce variabilities exceeding 20%. Here, we present a standardized protocol that transforms water uptake measurements from rough estimates into precise, comparable "hydration fingerprints." By replacing manual wiping with a calibrated pressure-blotting rig (0.44 N cm^-2 for 10 s twice) and verifying both dry and wet states via ATR-FTIR spectroscopy, we dramatically reduce scatter and align our FAAM-PK-75 (<i>Fumatech</i>, <i>Bietigheim</i>, <i>Germany</i>) results with published benchmarks in DI water, aqueous KOH (0.1-9 M), various alcohols, and controlled humidity (39-96% RH). These uptake profiles reveal how OH^- screening, thermal densification at 60 °C, and PEEK reinforcement govern equilibrium hydration. A low-cost salt-bath method for vapor-phase sorption further distinguishes reinforced from unreinforced architectures. Extending the workflow to additional commercial and custom membranes confirms its broad applicability. Ultimately, this work establishes a new benchmark for AEM hydration testing and provides a predictive toolkit for correlating water content with conductivity, dimensional stability, and membrane-ink interactions during catalyst-coated membrane fabrication.